Protection of well casing from thermal overstressing



July 22, 1969 R. DEAN ET AL 3,456,734

PROTECTION OF WELL CASING FROM THERMAL OVERSTRESSING Filed Jan. 5, 1968 WATER INVENTORS M. R. DEAN BY J. C TRANTHAM A TTORNEYS United States Patent 3,456,734 PROTECTION OF WELL CASING FROM THERMAL OVERSTRESSING Maurice R. Dean and Joseph C. Trantham, Bartlesville,

Okla, assignors to Phillips Petroleum Company, a

corporation of Delaware Filed Jan. 5, 1968, Ser. No. 696,015 Int. Cl. EZlb 43/24, 43/00 US. Cl. 166-302 8 Claims ABSTRACT OF THE DISCLOSURE Excessive, thermal stressing of a casing in a well during injection of hot fluid, e.g., steam, is prevented by periodically discontinuing injection of the hot fluid, e.g., steam, and injecting water into an annulus formed between the hot fluid injection pipe and the casing, which are usually provided in such a well. The disclosed operation is applied to steam injection wells in production of below-ground materials such as hydrocarbon oils. The coolant can be used for heat transfer to the formation or at the surface as desired and control can be effected based upon steam temperature and injection of steam time. Coolant is injected at a preselected temperature which is reduced at a selected and controlled rate to a selected lower value as injection of it proceeds.

This invention relates to the protection of a well casing from thermal overstressing. In one of its aspects it relates to the protection of a well casing from thermal overstressing when steam injection is being employed for use in a formation well below the ground as in production of a material from below ground which it is desired to heat, e.g. oil. In a further aspect the invention relates to the operation of a direct drive or a so called huff and puff" steam stimulation production operation as practiced in oil production.

In one of its concepts, the invention provides a method in which after a period of time of injection of hot fluid, e.g. steam, through a tubing within a well casing, coolant, e.g. water, at a desired and preferably elevated temperature is pumped through the annulus to progressively and controllably cool the casing to a temperature such that steam injection can be and is resumed. In another of its concepts the invention relates to such an operation wherein the coolant is passed into the formation. In a further concept the invention provides such an operation in which the coolant is withdrawn from the well annulus and is utilized above the ground or at least at a level above the formation being produced.

In some oil-producing wells it is desirable to inject steam to stimulate the oil-producing rate. Steam generally cannot be injected down the casing because the increase in the temperature of the casing metal can cause the casing to buckle and even to break, thus interfering with subsequent production operation. In order to prevent casing damage, the steam is usually injected through tubing placed concentrically inside the casing with a packer at the bottom. The gas-filled annulus serves to reduce the rate of heat flow from tubing to casing thus allowing a larger total amount of heat to be passed through the tubing before the casing temperature reaches a safe upper limit. Considerably more steam can be thus passed into and through the tubing than can be done when the steam is in direct contact with the casing. However, even when using tubing, the steam injection must often be terminated before the desired amount of steam has been injected. To remedy this situation, it has been proposed to surround the steam injection pipe with another pipe to create an enclosed space in which a vacuum can be drawn for in- "ice sulation purposes. Thus, there is placed into ,the well casing a double injection pipe, so to speak. In the annulus thus formed a coolant such as water is pumped continuously down into and up and out from the well casing. Such a system is elaborate, expensive and the coolant is found to be working against the steam during steam injection. It is also known to surround an injection pipe with a coolant resting within the casing surrounding the injection pipe the coolant being so selected that due to heat it will evaporate, condense in the upper regions of the casing and flow back down into the lower portions of the casing, thus cooling the same. Such a system requires the constant presence of the coolant and, again, the coolant is acting against the steam or other heating fluid which is being injected.

I have now discovered an improved method of injecting steam through a tubing located within the casing. I inject steam for a period of time such that the casing temperature reaches a preselected upper limiting value. Then steam injection is terminated and liquid water or other coolant at a preselected maximum temperature is injected into the annulus in the casing. The temperature of the injected water is reduced at a selected and controlled rate and the rate of injection is controlled to a selected value. Water injection is thus continued until the casing temperature has been reduced as quickly as is reasonable to a desired lower level at which time water injection is discontinued and steam injection again resumed. The cycle of steam-coolant-steam etc. is repeated until the total desired amount of steam has been injected.

It is an object of this invention to provide a method for preventing thermal overstressing of a well casing. It is another object of this invention to provide an improved method for injecting a heating fluid into a well. It is a further object of this invention to provide a method for heating a formation below ground. It is a still further object of this invention to provide an improved method of producing a material from below ground, e.g. oil.

Other aspects, concepts and objects of the present invention are apparent from a study of this disclosure, the drawing and the appended claims.

According to the present invention, there is provided a method of injecting a heating fluid into a formation below ground which comprises providing within a casing in a well an injection tubing thus creating an annulus, injecting heating fluid through said tubing until a desired maximum temperature of the casing has been attained, then discontinuing injection of heating fluid through said tubing, then the injection through said annulus of a coolant at a maximum temperature such that the casing will not be unduly stressed by change of temperature, continuing the injection of the coolant, preferably at a gradually reduced temperature, and at a rate such that the desired cooling of the casing will take place, then discontinuing injection of coolant and re-commencing injection of heatant until such time as the desired amount of heat has been transmitted into said formation.

The invention will now be described in connection with production of oil from an oil bearing formation. The invention is applicable to buff and puff steam injection as well as to direct drive steam injection operations as these are well known and understood in the oil industry. The invention is also applicable to the production of other materials from below ground by injection of heat as by, for example, steam in the production of sulfur, salt and other minerals.

In the drawing there is shown an embodiment of the invention.

Referring now to the drawing, there is provided in a casing 1 a substantially concentrically disposed injection tubing tube 2. Steam is cyclically injected through tubing 2 by way of pipe 4 and passes into the producing formation 5. Whenever the casing temperature has reached a point beyond which it is not desired to take the same, injection by way of pipe 4 is discontinued and water is injected by way of pipe 6. As shown in the drawing, packer 3 is provided in which case the water, after having gone down to approximately the level of the formation can be either removed from the casing to the ground surface or to a higher level or passed into the formation. In the event the water is to be passed into the formation, it can pass through a disposal point in packer 8 as shown. If desired, the disposal point 8 in packer 3 can be closed. The water can be injected through an extension of pipe 6 into the bottom of the well just above the packer and removed from above the packer and from the well by way of pipe 7 which, in one form, can be and is an overflow pipe. In another form of the invention, water is fed to the top of the casing through pipe 7, 'fiows downwardly to just above the packer and is removed from the bottom of the well by way of pipe 6 at a point just above the packer 3. In the now preferred embodiment of the invention, the latter operation is employed. Thus, the water enters into the top of the well and passes progressively down into the well and from the bottom of the well upwardly through pipe 6 as shown.

EXAMPLE With ground and well casing temperature initially at 100 F., there are needed 100 hours of 600 F. steam injection to raise the casing temperature to 380 F. Steam injection is then stopped. The casing tubing annulus is filled with water and circulation of 100 F. water initiated to cool the casing. Circulation of 430 barrels a day for five days will bring the casing temperature to 273 F. Injection of steam is again initiated and the process repeated. (The Water circulation was calculated on the basis of filling the well casing annulus twenty times and taking ofif water after the equilibrium temperature had been reached. Water withdrawal temperatures vary from 370 F. to 273 F.) The circulation given is for a Well 3000 feet deep and a casing 6 /2 inches internal diameter. The water is injected into the annulus formed between the steam injection tubing and the casing. This annulus has an approximate cross-sectional area of 24 square inches.

From the foregoing description, it is apparent that there has been provided an improved method for cooling a casing to prevent thermal overstressing thereof and in said method variance depending upon the heat transfer and handling of coolant desired.

One skilled in the art in possession of this disclosure having studied the same will understand that a very simple apparatus is required for practicing the operation of the invention and that during the time from when the preferred embodiment, when there is no water in the annulus, the annulus can be gas filled so that the gas acts as a heat transfer barrier. Thus, gas can be injected by pipe 9 while pipe 7 is shut off and gas injection continued until gas emanates from pipe 6, indicating that the annulus is now gas filled. Other heat transfer barrier materials can be used in the annulus during stream injection and when water circulation is arrested. Thus, a liquid which readily evaporates to fill the annulus with an insulating vapor barrier can be used as one skilled in the art will understand. Such a liquid can be a low-boiling point hydrocarbon as available and as the case may be.

Reasonable variation and modification possible within the scope of the foregoing disclosure, the drawing and the appended claims of the invention, the essence of which is that there have been provided a method for protection of a well casing from thermal overstressing, the steps of the method com-prising in combination providing an injection tube within the well casing thus forming an annulus, injecting a heatant through the tube until the temperature of the casing which it is not desired to exceed has been reached, discontinuing injection of heatant and injecting coolant into and through the annulus, in one embodiment the coolant being passed into the formation and in another at least a portion thereof being removed from the casing as described; in a further embodiment a vapor barrier within the annulus being provided during heatant injection.

We claim:

1. A method for protecting a well casing from thermal overstressing during injection of a heatant into a formation into which the well casing extends which comprises in combination the steps of providing an injection tubing disposed within said casing, thus forming an annulus, injecting heatant through said tubing until the casing temperature which it is desired to not exceed has been reached, discontinuing the injection of heatant, commencing the injection into the annulus of a coolant and removing the coolant from said annulus.

2. An operation according to claim 1 wherein alternately heatant and coolant are passed as described until a desired temperature of the formation has been reached.

3. An operation according to claim 1 wherein the used coolant is passed into the formation.

4. An operation according to claim 1 wherein the used coolant is passed down through the annulus to the bottom of the well and upwardly therefrom and removed at an upper level from the well.

5. An operation according to claim 4 wherein said up per level is at ground surface.

6. An operation according to claim 1 wherein the used coolant is pumped into the bottom of the well and upwardly through the annulus for removal at the top of the well.

7. A method according to claim 1 wherein steam is the heatant and water is the coolant and the water is passed into the formation.

8. An operation according to claim 1 wherein steam is the heatant and water is the coolant and the coolant is passed downwardly through the annulus to the bottom of the casing and then passed from there upwardly through the casing to an upper level as at the ground surface.

References Cited UNITED STATES PATENTS 1,237,139 8/1917 Yeomans 16611 3,042,114 7/1962 Willrnan 166-11 3,142,336 7/1964 Doscher 166l1 3,180,411 4/1965 Parker 166-11 3,280,909 10/1966 Closmann et a1. 16611 3,358,759 12/1967 Parker 16611 3,380,530 4/1968 McConnell et al 16640 3,386,512 6/1968 Bloom l 166-40 STEPHEN J. NOVOSAD, Primary Examiner US. Cl. X.R. 166303 

